Malaria

Malaria is a parasitic disease passed on by mosquitoes in the tropics and subtropics. A single bite is enough. The parasite enters the blood, multiplies in the liver and then destroys red blood cells, at which point the fever starts. The essential point fits into one sentence: treated in time, malaria clears up without a trace; left alone, it kills within days. Fewer than twenty-four hours can separate feeling slightly unwell from being in danger of death, so a fever in someone back from the tropics is not a reason to lie down and wait but a reason to have a blood test the same day. And one thing more: taking preventive tablets lowers the risk but does not remove it, so "I took my antimalarials" does not excuse skipping the test.

How malaria is caught

The cause is a single-celled parasite, the plasmodium, carried by the female Anopheles mosquito. These mosquitoes bite at dusk and through the night rather than during the day, and they do not whine as noticeably as the ones we are used to. Malaria does not pass from person to person by ordinary means: not by a handshake, not by sharing crockery, not through the air. The exceptions are rare and specific: blood transfusion, a needlestick injury, and passage from mother to baby during pregnancy.

People catch it in tropical Africa, South and South-East Asia, the Middle East, Oceania, Central and South America, Haiti and the Dominican Republic. The risk varies enormously not only between countries but within one country: in the capital or at a beach resort it may be nil, while in rural areas during the rainy season it is high. So before travelling the question is not whether the country is dangerous, but the particular region and the time of year.

One group deserves separate mention: people born in a country where malaria is common who have lived in Europe for years. The partial immunity they had as children fades over time. A trip home to see relatives is as risky for them and their children as for any other traveller, yet they are the least likely to take tablets before going.

Why malaria is dangerous

Several species of plasmodium infect humans, and they behave very differently. The most dangerous is falciparum malaria, which predominates in sub-Saharan Africa. In it the infected red cells stick to the walls of small vessels and block them, so the brain, the kidneys and the lungs suffer. This species accounts for almost all deaths, and it is the one that can turn "just a temperature" into a life-threatening illness within a day.

The species vivax and ovale run a milder course but have a quirk of their own: some of the parasites lie dormant in the liver and wake up months, sometimes a year or more, after the trip. By then the traveller has forgotten the journey and does not connect it with the fever, and the doctor, without that clue, does not think of malaria. So mention any trip to the tropics in the past year yourself, even if nobody asks.

There is also knowlesi, found in the forests of South-East Asia and acquired from monkeys; it multiplies very quickly and can also be severe. The species is identified on the blood test, and the choice of drug follows from it.

Early symptoms and when to expect them

Malaria starts non-specifically, and that is the trap: for the first few days it looks like flu or a stomach bug. There is a high temperature with shivering and drenching sweats, headache and aching muscles, exhaustion, nausea, tummy pain and sometimes diarrhoea and a cough. The textbook attacks every other day are usually absent at the start, so waiting for them is a mistake.

In children the picture is even harder to recognise: the child becomes floppy and sleepy, refuses food and drink, and may have only vomiting or only tummy pain without any striking fever.

Falciparum malaria usually declares itself one to two weeks after the bite, but never before the seventh day: a temperature on the third day home is almost certainly something else. The other species can produce a first attack months later. The general rule is simple: any fever within a year of returning from a malarial area counts as malaria until a blood test says otherwise.

When urgent help is needed

Call an ambulance (in European countries on the single number 112) if someone who has been in the tropics develops:

• confusion, marked drowsiness, delirium, fits, or cannot be roused;
• fast, laboured or noisy breathing, or breathlessness at rest;
• dark urine the colour of strong tea or cola, or hardly any urine at all;
• yellowing of the skin and the whites of the eyes;
• bleeding gums or nose, or bruises appearing without injury;
• extreme weakness, cold clammy skin, a fast weak pulse, an inability to stand;
• relentless vomiting that makes it impossible to drink or keep tablets down.

Small children and pregnant women deserve a line of their own: they deteriorate faster, and help should not be delayed.

If there is only fever and aching and none of the above, it still is not a case of waiting until Monday: see a doctor and have the blood test the same day. Say plainly where you were and when, because that changes the whole line of enquiry.

How the diagnosis is confirmed

The diagnosis is made on a drop of blood. The main method is microscopy of a thick and thin film: the parasites are seen directly, the species is identified, and the proportion of infected red cells is counted. That proportion matters as much as the finding itself, because it decides between treatment at home and admission to hospital.

There are also rapid tests that give an answer within a quarter of an hour from a fingerprick. They are convenient but less sensitive when parasite numbers are low, and they do not replace microscopy.

The crucial detail: a single negative result does not rule malaria out. Parasites enter the blood in waves, and between waves they may not be seen. So if suspicion remains, the test is repeated after 12 to 24 hours, and the diagnosis is only dismissed after several negative samples over two days. If you had one test, were told it was clear, and the fever persists, go back and ask for it to be repeated.

How it is treated

Malaria is curable and the drugs exist. Uncomplicated falciparum malaria is treated with artemisinin-based combinations taken by mouth over several days. Severe malaria is treated in hospital, starting with an intravenous drug, because tablets are useless when someone is vomiting or drowsy, and here a few hours of delay cost a great deal.

The choice of drug depends on the species and on the country where the infection was picked up: resistance patterns differ from region to region. That is why treatment is prescribed by a doctor rather than bought over the counter, and why it matters to describe the route of the trip precisely.

With the species that hide in the liver, clearing the blood is not enough: without a second drug that kills the dormant forms, the fever will return months later. Before it is prescribed, the G6PD enzyme is checked, because if that enzyme is deficient the drug destroys red blood cells. Skipping this second stage is not an option, even when you have felt perfectly well for a long time.

How to lower the risk on a trip

It is worth preparing in advance, ideally six weeks before departure, though a consultation a few days beforehand is still useful. The doctor will check the situation in the exact region you are heading for and choose preventive tablets. They are started before departure and must be continued after you get back; how long depends on the drug, and stopping early is not an option, because that is precisely when the parasites emerge.

The other half of the protection is not being bitten, and it works regardless of the tablets. Sleep under an insecticide-treated net if the room has no air conditioning and no screens on the windows. From dusk onwards wear long sleeves and long trousers. Put insect repellent containing DEET on exposed skin and reapply it as often as the label says; for children and in pregnancy use a suitable strength, which is worth asking about.

Particular care is needed by pregnant women, small children, older travellers, people whose immune system is weakened and people without a spleen: malaria is more severe in all of them. Pregnant women are usually advised not to travel to high-risk areas at all. The malaria vaccines now available are given to children in tropical countries where the disease is constantly present; for a traveller they replace neither tablets nor bite protection.

Online consultation

Two things are well suited to a remote consultation. The first is preparing for a trip: the doctor goes through your itinerary, says whether preventive tablets are needed in your case and which ones, taking account of long-term conditions, pregnancy and other medicines, explains when to start and when to finish the course, and checks what else is worth arranging before you fly.

The second comes after you are back. If a fever appears, the doctor weighs the symptoms and the dates of the trip to judge how likely malaria is and, above all, says where to go for the blood test, how quickly, and exactly what to ask to have checked. What cannot be managed by message is the fever itself in someone home from the tropics: here the laboratory makes the diagnosis, and it is needed today rather than next week. The doctor will also spell out the signs that mean calling an ambulance instead of writing.

This material is for information only and does not replace medical advice.